A conventional DC (direct current) offset canceller, which uses an SAR (Successive Approximation Register) and is used for wireless communication, determines whether an output of VGA (Variable Gain Amplifier) is greater than or smaller than 0 by a comparator, and performs DC offset cancellation with an SAR algorithm by using the determination result.
In the conventional method, when the gain of LNA (Low Noise Amplifier) and the VGA is low, the output signal of the VGA (that is, input signal to the comparator) is not affected by noise input into the LNA, and the DC offset cancellation is performed correctly. However, when the gain of the LNA and the VGA is high, the noise input into the LNA is amplified and the output signal of the VGA fluctuates largely in both positive and negative directions, so that the influence of the noise cannot be ignored. For example, if a result of comparator is used at a timing when the output signal of the VGA fluctuates in the positive direction, a DC offset value is erroneously calculated to be positive by the algorithm of SAR even though the actual DC offset value is negative. As a result, there is a problem that the DC offset canceller does not operate correctly and the DC offset is not cancelled.
For example, a DC offset canceller described in Japanese Patent Application Laid-Open No. 2006-108844 is known.